Electric Machine with Rotor Magnet Tabs

The present application claims priority from United States provisional patent application number 63/695,988, filed Sep. 18, 2024, the entire contents of which are incorporated by reference herein.

The present disclosure relates to the field of electric machines, and more particularly, electric motors for electric vehicles.

Interior permanent magnet electric machines have been widely used as driving and generating machines for various applications, including electric and hybrid-electric vehicles. Internal permanent magnet (IPM) electric machines have magnets built into the interior of the rotor. Typically, each magnetic pole on the rotor is created by putting permanent magnet (PM) material into one or more slots formed in the laminated stack of the rotor. Although slots are formed for the magnets, the slots are typically not completely filled with magnetic material. In particular, the slots are typically longer than the magnets, and the magnets are placed in the center portion of each slot. This results in a slot with a magnet in the center and voids at two opposite ends of the slot.

There are several reasons for shaping slots longer than the magnets such that voids are provided at the ends of the slots. Examples of such reasons include issues related to performance of the electric machine and manufacturing issues. These issues are discussed in U.S. Pat. No. 7,851,958 , issued Dec. 14, 2010, the entire contents of which are incorporated by reference herein.

In electric machines wherein the magnets that are shorter than the slots, features must be utilized to maintain the proper position of the magnets within the slots. Without such stabilizing features, the magnets tend to slide between the voids at the ends of the slots. Unfortunately, the use of stabilizing features in an IPM machine can affect the magnetic fields within the machine. If care is not taken in the design of the IPM machine, situations can occur where the magnetic fields can demagnetize the permanent magnets over time. Irreversible demagnetization of the permanent magnets can lead to decreased performance of the electric machine.

Accordingly, it would be desirable to provide an IPM electric machine with stabilizing features for magnets within the electric machine. It would also be desirable if such stabilizing features did not adversely affect the magnetic fields and related magnetic properties in the electric machine which might lead to demagnetization of the machine's permanent magnets. Furthermore, it would be desirable if such stabilizing features could be provided at a relatively small increase in manufacturing costs.

7 FIG. In at least some prior art electric machines, straight tabs are provided in the slots of the rotor in order to apply pressure to the magnets against the outer wall of the magnet slot. However, as illustrated in, when magnets are inserted into slots with tabs, the straight tabs tend to scrap off the protective coating on the magnets. This damage to the magnets may result in diminished magnet performance over time.

In view of the foregoing, it would be advantageous to provide an electric machine that is configured to retain magnets in the magnet slots on the rotor but avoids the expense of epoxy in the slots. It would also be advantageous to provide a method of making such an electric machine that did not result in scraping of the protective coating on the magnets.

An electric motor and associated method of making an electric motor is described herein. The method of making the electric motor includes pre-bending a tip of a tab that extends into the rotor slot such that the portion of the tab which contacts the magnet is not a sharp edge. No epoxy is required to retain the magnet in the slot. Therefore, the problem of epoxy cost with some prior art magnets is solved by eliminating the epoxy. Also, the problem of magnet coating damage (i.e., scraping) is solved by eliminating the tab's sharp edge contacting the magnet.

In at least one embodiment, an electric machine includes a stator having a plurality of windings and a rotor positioned within the stator. The rotor includes a lamination stack formed from a plurality of lamination sheets with a plurality of slots formed in the lamination stack. The rotor further includes a plurality of magnets arranged in the plurality of slots. At least one of the plurality of lamination sheets includes a tab extending into an associated one of the plurality of slots, the tab including a bent distal tip defining a distal curved surface and a bent proximal joint defining a proximal curved surface, wherein the distal curved surface engages one of the plurality of magnets positioned in the associated one of the plurality of slots.

In another embodiment of the disclosure, a rotor for an electric machine includes a plurality of magnets and a lamination stack formed from a plurality of lamination sheets. A plurality of slots are formed in the lamination stack and at least one magnet of the plurality magnets is positioned in an associated slot of the plurality of slots. At least one lamination sheet of the plurality of lamination sheets includes a tab extending into the associated slot, the tab including a distal curved surface and a proximal curved surface. The distal curved surface engages the magnet within the associated slot, and the proximal curved surface is separated from the magnet within the associated slot.

In yet another embodiment, a method is disclosed for securing magnets within an electric machine. The method includes forming a core of the electric machine comprising a lamination stack formed of a plurality of lamination sheets, the lamination stack defining a plurality of slots configured to receive a plurality of magnets, wherein at least one of the plurality of lamination sheets includes at least one tab extending into an associated slot of the plurality of slots. The method further include pre-bending the tab prior to insertion of a magnet into the associated slot. Thereafter, the method includes inserting a magnet into the associated slot, wherein the tab is further bent during insertion of the magnet into the associated slot.

The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. While it would be desirable to provide an electric machine that provides one or more of these or other advantageous features as may be apparent to those reviewing this disclosure, the teachings disclosed herein extend to those embodiments which fall within the scope of the appended claims, regardless of whether they include or accomplish one or more of the advantages or features mentioned herein.

In the following description, an electric machine is disclosed with a rotor including magnet pockets having tabs arranged therein. The rotor is manufactured by preparing a lamination stack wherein straight tabs are stamped into special laminations that are periodically arranged on the lamination stack. The tabs are pre-bent near their tips prior to magnet insertion. When a magnet is inserted into the magnet pocket, the tabs are further bent without damaging the magnet. The bent tabs hold the magnet to the outer edge of the magnet pocket.

In the following detailed description, reference is made to the accompanying figures which form a part hereof wherein like numerals designate like parts throughout, and in which is shown, by way of illustration, embodiments that may be practiced. It is to be understood that other embodiments may be utilized, and structural or logical changes may be made without departing from the scope of the present disclosure. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of embodiments is defined by the appended claims and their equivalents.

Aspects of the disclosure are disclosed in the accompanying description. Alternate embodiments of the present disclosure and their equivalents may be devised without parting from the spirit or scope of the present disclosure. It should be noted that any discussion herein regarding “one embodiment”, “an embodiment”, “an exemplary embodiment”, and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, and that such particular feature, structure, or characteristic may not necessarily be included in every embodiment. In addition, references to the foregoing do not necessarily comprise a reference to the same embodiment. Further, irrespective of whether it is explicitly described, one of ordinary skill in the art will readily appreciate that each of the particular features, structures, or characteristics of the given embodiments may be utilized in connection or combination with those of any other embodiment discussed herein.

Additionally, it will be noted that the following description of embodiments of an electric machine with rotor magnet tabs makes use of relative terms that may be dependent on an orientation of the structure at a given time (e.g., during manufacture or use of the machine in a vehicle). Accordingly, it will be recognized that many terms of orientation and position as used herein are defined with reference to what may be shown in the drawings and/or other common positions. While efforts have been made herein to reference portions of a structure with respect to non-changing features (e.g., “axial,” “radial” and “circumferential” directions and related positions of the stator), it will be recognized that other terms are relative terms that depend on the position of the structure (e.g., “vertical,” “horizontal,” “upward,” “downward,” “top,” “bottom,” etc.).

1 FIG. 1 FIG. 10 12 20 12 30 20 32 With reference to, a partial cross-sectional view of an electric machine is shown. The electric machinecomprises a statorand a rotoropposing the stator. A plurality of slotsare formed in the rotor, each of the plurality of slots are configured to hold a permanent magnet. It will be appreciated by those of ordinary skill in the art thatshows only about 45° of the rotor and stator arrangement for the sake of simplicity, but the rotor and stator arrangement actually extends 360° to form a complete circular rotor and stator arrangement for the electric machine.

12 13 13 14 16 20 16 12 18 12 16 19 18 12 1 FIG. The statorincludes a main body portion provided by of a stack of lamination sheetscomprised of magnetic-permeable material, such as silicon steel or a ferromagnetic material. The partial cross-sectional view ofillustrates the general disc shape for one lamination of the stator lamination stack. The stator itself is also generally disc shaped and includes a circular or polygonal outer perimeterand a circular inner perimeter. An inner cavity configured to receive the rotoris formed within the inner perimeterof the stator. Winding slotsare formed in the stator. Openings to the winding slots are provided at the inner perimeterof the stator. Conductorsare placed in the winding slotsto form armature windings for the electric machine on the stator.

20 23 21 21 23 21 60 21 23 20 20 23 26 12 26 20 16 12 22 12 20 20 12 1 FIG. The rotoralso includes a main body portion provided by a stackof lamination sheetscomprised of magnetic-permeable material, such as silicon steel or a ferromagnetic material. The partial cross-sectional view ofillustrates the general disc shape for one lamination sheet(which may also be referred to herein as simply a “lamination”) of the rotor lamination stack. The laminationsare all generally the same size and shape, but at least one lamination of the lamination stack includes a magnet retaining tab, as explained in further detail below. When the laminationsare stacked on top of one another, the lamination stackis formed, which provides a core for the rotor. The general shape of the rotoris defined by the lamination stackand includes a circular outer perimeter. The rotor is designed and dimensioned to fit within in the inner cavity of the statorsuch that the circular outer perimeterof the rotoris positioned opposite the circular inner perimeterof the stator. A small air gapseparates the statorfrom the rotor, and the rotoris configured to rotate relative to the stator.

20 30 32 30 20 34 36 38 34 30 32 60 34 30 32 34 32 34 32 32 34 30 20 36 38 30 36 38 36 38 36 38 34 36 38 1 FIG. The rotorincludes a plurality of magnet pocketsconfigured to retain permanent magnets(which magnet pockets are also referred to herein as “magnet slots” or simply “slots”). Each magnet slotin the rotorincludes a central magnet retaining portionpositioned between two opposing end portions,. The magnet retaining portionof each slotis designed to retain a magnet. As explained in further detail below, at least one magnet retention tabextends into the central magnet retaining portionto assist in retaining the magnet in the slot. The magnetsin the embodiment ofare generally rectangular in shape, and thus the magnet retaining portionassociated with each magnetis similarly rectangular in shape. The magnet retaining portionis also slightly larger than the magnetsuch that the magnetmay be inserted into the associated magnet retaining portionof the slotduring assembly of the rotor. The opposing end portions,of each slotare non-ferromagnetic portions. These non-ferromagnetic portions are designed to remain empty, providing voids in the opposing end portions,. However, in at least some embodiments, the opposing end portions,may be filled by non-magnetic-permeable materials, such as nylon. In each case, the end portions,provide two non-ferromagnetic portions with the magnet retaining portionof the slot positioned between the non-ferromagnetic portions,.

1 FIG. 1 FIG. 30 20 30 12 20 30 40 40 42 42 40 30 26 42 30 30 30 In at least one embodiment, such as that shown in, the slotsin the rotorare configured in a nested V-shaped slot arrangement comprised of two V-shaped slot arrangements with a first V-shaped slot arrangement positioned within a second V-shaped slot arrangement. Each slotprovides one of two opposite legs of one V-shape arrangement. Each V-shaped slot arrangement includes a mouth end that opens toward the statorand a vertex end (or tip end) that is closer to a center of the rotorthan the mouth end. Each slotthat forms a leg of one of the V-shaped slot arrangement includes two elongated sides. The two elongated sides of each slot include an inner-V side(also referred to herein as a stator side) and an outer-V side(also referred to herein as an opposing side). Accordingly, the stator sideof the slotgenerally opposes the outer peripheryof the rotor, and the opposite sideof the slotgenerally opposes an inner periphery of the rotor (or center axis defined by the rotor). In the embodiment of, the slotsare completely separated at the tip end of the V-shaped slot arrangement, such that two separate slots form the V-shaped slot arrangement. In this embodiment, the elongated sides of different slots do not connect together. However, in other embodiments, the slotsof each V-shaped slot arrangement may merge together.

50 52 30 50 52 34 36 38 50 52 32 50 52 In the embodiment disclosed herein, magnet locators,are also arranged at the ends of the slots. The portion of the slot between the magnet locators,defines the central magnet retaining portion; the void portions (i.e., the non-magnetic-permeable portions) that border the central magnet retaining portions define the end portions,of the slot. The magnet locators,are spaced in the slot such that they fit up against opposing shorter ends of the magnetto be placed in the slot. Accordingly, with the magnet locators,, the slot is configured such that the shape of the slot helps to retain the magnet in its proper position once it is inserted in the slot.

32 34 30 40 42 30 32 50 52 34 32 30 As noted previously, the magnetsare generally rectangular in shape and are designed to fit within the central magnet retaining portion. Accordingly, each rectangular magnetincludes two elongated sides which abut or are in close proximity to the elongated sides,of the slot. The magnetalso includes two shorter sides that abut or are in close proximity to the magnet locators,at the boundary of the central portion. Thus, all four sides of the rectangular magnet abut or are in close proximity to a solid surface, and this arrangement helps secures the magnetin place within the slot.

2 3 FIGS.-C 2 3 FIGS.-C 5 FIG. 21 21 23 60 34 30 60 21 21 21 30 60 60 30 21 21 60 30 21 60 20 21 60 21 60 60 60 a a a a a a a a With reference now toat least one laminationof the plurality of laminationsof the lamination stackincludes a tabthat extends into the magnet retaining portionof an associated magnet slot. The tabis integrally formed with the other features of the laminationwhen a sheet of magnetic-permeable material is stamped (or otherwise made) in order to form the lamination. It will be recognized that each laminationis a monolithic sheet of material that provides all components of the sheet including the slotsformed therein and any associated tabs. Each tabis a generally narrow and flat finger-like member that projects into the slotand is defined by a thickness that is the same as or substantially the same as the remainder of the lamination sheet. While a single laminationwith a tabthat extends into the slotis illustrated in, it will be recognized that several laminationswith tabsare anticipated in different embodiments of the rotor. For example, in at least one embodiment, at least every fifth lamination is a laminationwith tabs(e.g., each laminationwith tabsis stacked on top of a series of seven to ten additional laminations with no tabs). The tabsmay be arranged in columns within the slots, similar to the column of tabsshown in.

2 3 FIGS.-B 3 FIG.A 3 FIG.C 3 FIG.A 60 21 20 21 60 60 60 60 30 60 21 60 62 72 62 30 72 30 30 60 72 60 74 60 32 74 60 a a a a a a a With continued reference to, the tabsof the laminationsundergo a formation process during manufacture of the rotorfrom an initial stamped condition (shown in) to a final completed condition (shown in).shows the lamination sheetwith the tabin a pre-assembly/initial conditionfollowing stamping of the lamination sheet. In this initial condition, the tabis provided as a straight, narrow, flat finger structure that extends directly into the slot, and the entire tabis parallel to the rest of the lamination sheet. The tabincludes a proximal endand a distal end. The proximal endis near a perimeter edge of the slot. The distal endprojects outward in a peninsula-like manner into the slotand does not engage any components within the slotwhen in the initial condition. Accordingly, the distal endof the tab may be considered a “free edge” in the initial condition. The distal perimeter edgeof the tabis a relatively sharp edge formed from stamping of the lamination (and may also be referred to herein as a “stamped edge”) or other manufacturing process. In order to protect the magnetfrom this sharp distal perimeter edge, further manipulation of the tabis performed during the manufacturing process, as explained in further detail below.

3 FIG.B 3 FIG.B 2 FIG. 2 FIG. 2 3 FIGS.andB 3 FIG.A 72 60 32 60 72 62 60 72 76 78 60 62 30 78 60 74 60 60 78 62 60 74 60 74 60 b b b a As shown in, the distal endof the tabis pre-bent prior to installation of the magnetin the slot. In this pre-bent/intermediate condition, the distal endis generally bent about 90° (e.g., between 85° and 95°) relative to the proximal end. Following the pre-bend process of, the tabincludes a distal endwith a first/distal curved surface. As a result, the end tipof the tabdefines a flat surface that is generally perpendicular to the proximal end(e.g., generally vertical) and therefore parallel to the perimeter walls of the slot. The arrangement of the surface of the tipis best illustrated in. As shown in, the perimeter of the tabat the stamped edgeis generally perpendicular to the slot walls when the tabis in the pre-bent configuration. It words, the distal end tipthat is generally perpendicular to the proximal end. Accordingly, when in the pre-bent condition(shown in), the sharp stamped edgeof the tabis diverted away from the outwardly exposed position of the stamped edgewhen in the initial condition(shown in).

3 FIG.C 2 FIG. 2 FIG. 2 FIG. 32 30 20 60 62 60 60 60 62 60 30 66 76 74 68 60 66 76 66 76 66 76 66 76 68 32 30 76 32 66 c As shown in, when the magnetis inserted into the slotduring manufacture of the rotor, the magnet further bends the tabcloser to the proximal endof the tab. In this assembled/final condition, an additional curvature is formed in the tabat a bent proximal joint positioned closer to the proximal endof the tabnear the perimeter wall of the slot. This additional curvature is best illustrated inby proximal curved surfaceformed inwardly from (i.e., on a proximal side of) the distal curved surfaceand the distal perimeter edge. Whileshows a length of flat sectionon the tabbetween the proximal curved surfaceand the distal curved surface, it will be recognized that in some embodiments, the proximal curved surfacemay be so close to the distal curve surfacethat the proximal curved surfaceis integral with the distal curved surface(i.e., in other words, the proximal curved surfacebleeds into the distal curved surfacewith no flat sectiontherebetween). As also shown in, once the magnetis inserted into the slot, the distal curved surfaceengages the magnetand the proximal curved surfaceis separated from the magnet by a short distance d.

32 30 76 60 32 60 30 32 Once the magnetis fully inserted into the slot, the distal curved surfacesof the tabspress against one side of the magnetand force another side of the magnet into close engagement with an edge of the slot. This results in a strong friction-fit for the magnetwithin the slot. In at least some embodiments, no additional material is used to secure the magnets in the slots. In other embodiments, epoxy or other adhesives may be used to further secure the magnetin the slot.

4 4 FIGS.A-D 4 FIG.A 4 FIG.A 5 FIG. 5 FIG. 20 10 30 21 60 21 21 60 30 30 60 30 60 30 a a With reference now to, a method of making a rotorfor an electric machineis illustrated.shows one slotof a lamination stack with a plurality of laminationsincluding tabs(also referred to herein as “special laminations”). Each special laminationis positioned on top of a series of seven regular laminationsthat do not include tabs. As shown in, the lamination stack is formed with the special laminations in the “initial condition” discussed above, wherein each tab is flat and extends in a radial direction into the associated slot.shows an enlarged perspective view looking downward into a magnet slotwith a column of tabspositioned in the slot. As shown in, each of the tabsis in the initial condition with each tab in a flat condition and projecting outward into the slot.

60 60 60 60 80 80 82 92 82 30 60 82 84 86 84 84 86 86 82 60 30 86 82 60 30 4 FIG.B 6 6 FIGS.A-C After the lamination stack is formed with the tabsin the initial condition, the tabsare bent to the “pre-bent condition” discussed above, and as shown in. In at least one embodiment, the tabsare bent into the pre-bent condition using insert tooling configured to bend the tabsfrom the initial condition to the pre-bent condition. An exemplary insertion toolconfigured to perform the pre-bending process is shown in. The insertion tool(which may also be referred to as a “forming tool”) is a two-part component that includes a bending blockthat is freely moveable relative to a die block. The bending blockis an elongated post-like structure configured to extend into the magnet slotbetween two columns of tabspositioned within the slot. The bending blockincludes an elongated base portiondefined along an axis (e.g., a vertical axis) with a plurality of pegsthat extend perpendicularly outward from the base portion(e.g., in the horizontal direction). The elongated base portionhas a substantially rectangular cross-section with four generally flat sides. The pegsextend outwardly from one of the flat sides. The number of pegson the bending blockis equal to the number of tabsin a column of tabs within the slot. The pegsare periodically spaced apart on the bending blockto match the spacing of the tabswithin a column of tabs within the slot.

92 80 94 96 94 94 92 96 94 98 96 86 82 96 92 60 30 96 92 60 30 The die blockof the insertion toolincludes an elongated postwith a plurality of dies provided by hook-shaped structuresextending from the post. The elongated posthas a substantially rectangular cross-section with three generally flat sides. One of the flat sides of the die blockabuts and is configured to slide relative to one of the flat sides of the bending block, as explained in further detail below. Each of the hook-shaped structuresextends perpendicularly outward from the postand then curves upward to a position that is parallel to the post. A forming surfaceis provided along an interior surface of each hook-shaped structure. Similar to the pegsof the bending block, the number of hook-shaped structureson the die blockis equal to the number of tabsin a column of tabs within the slot, and the hook-shaped structureare periodically spaced apart on the die blockto match the spacing of the tabswithin a column of tabs within the slot.

80 82 92 86 96 92 84 82 94 92 In operation of the forming tool, the bending blockis positioned alongside to the die blockwith the pegsof the bending block positioned in the interior space defined by the hook-shaped structuresof the die block. Additionally, a flat surface of the elongated base portionof the bending blockis moved into slidable engagement with a flat surface of the postof the die block.

60 80 30 82 60 92 60 82 92 82 83 86 60 92 93 96 60 6 FIG.A In order to pre-bend the tabsin a column of tabs of a given slot, the forming structureis inserted into the associated slotwith the bending blockon one side of the column of tabsand the die blockon the opposite side of the column of tabs. Then, as shown in, the bending blockand the die blockare moved toward one another and into engagement with one another. Specifically, the bending blockis moved in the direction of arrowsuch that each pegis positioned above an associated tab, and the die blockis moved in the direction of arrowsuch that each hook-shaped structureis positioned under an associated tab.

82 92 60 82 92 85 86 82 60 98 96 92 60 98 6 FIG.B 4 FIG.A 4 FIG.B After the bending blockand the die blockare positioned adjacent to one another, the method of bending the tabsfrom the initial condition to the pre-bent position continues when the bending blockis slid downwardly relative to the die block, as illustrated by arrowin. As a result of this movement, the pegsof the bending blockforce the tabsinto engagement with the forming surfacesof the hook-shaped structureson the die block. This results in all of the tabsin a column being bent around the curved forming surfaceand re-configured from the initial condition (as shown in) to the pre-bent condition (as shown in).

60 80 82 92 87 97 80 30 80 6 FIG.C With all the tabsin a column re-configured to the pre-bent configuration, the method then continues by retracting the forming structurefrom the column of tabs. This is accomplished by simply moving the bending blockaway from the die block, as noted by the arrowsandin. The insertion toolis then be pulled out of the slot. Thereafter, the insertion toolmay be repositioned adjacent to another column of tabs for reconfiguration of the tabs from the initial condition to the pre-bent configuration.

60 32 30 30 68 60 72 30 32 76 32 60 60 74 60 32 30 60 60 32 30 30 4 4 FIGS.C andD 2 FIG. 4 FIG.C 4 FIG.D Once all of the tabsin a slot are moved to the pre-bent configuration, the method of forming a stator continues by inserting a magnetinto the slot, as illustrated in(and also illustrated in). As the magnet is first inserted into the slot, the bottom edge of the magnet first engages a flat sectionof the uppermost tabat a location adjacent the distal endof the tab, as shown in. Then, as the magnet continues to slide into the slot, the magneteventually reaches the distal curved surfaceand slides along the curved surface. As the magnetslides along the curved surface, the tabis further bent downwardly. In some embodiments, the tabsmay be bent downwardly until the distal perimeter edgeengages the sidewall of the slot. In other embodiments, the tabsare bent downwardly but do not bend to the extent that they engage the sidewall of the slot. As the magnetis forced further into the slot, it engages successive tabs, and bends those tabsaccordingly, until the magnetis fully inserted into the slotas shown in. Advantageously, because the magnet never encounters a sharp edge of the tab, no damage is done to the magnet as it slides into the slot.

32 30 60 32 60 30 60 30 As noted previously, once the magnetis fully inserted into the slot, the tabspress against one side of the magnetand force another side of the magnet into close engagement with an edge of the slot. This results in a strong friction-fit for the magnetwithin the slot. In at least some embodiments, multiple columns of tabsare included in each slot, and the different columns of tabs act in to force the magnet into a proper position in each slot and retain the magnet within each slot.

60 60 5 FIG. It will be recognized that various adaptations and embodiment of the electric machine and associated method are possible. In at least one embodiment, the tabsare stamped straight at the time of stamping the lamination, then pre-bent as single laminations, and then stacked into the lamination stacks. In at least one alternative embodiment, tabsare stamped straight, stacked into laminations stacks (e.g., with approximately every five to fifteen laminations having a tab). The tabs are then pre-bent prior to magnet insertion using with tooling like that shown in.

Although the various embodiments of an electric machine with a rotor magnet tab have been provided herein, it will be appreciated by those of skill in the art that other implementations and adaptations are possible. Furthermore, aspects of the various embodiments described herein may be combined or substituted with aspects from other features to arrive at different embodiments from those described herein. Thus, it will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by any eventually appended claims.